The present invention relates generally to the field of electrical connectors, and more particularly to electrical connectors for interconnecting various types of printed circuit boards having a multiplicity of individual circuits thereon.
It has long been well known in various electronics applications, such as computers and other complex electronic equipment, to interconnect printed circuit boards which perform specific functions in the application, and which, from time to time, must be disconnected for various reasons. For example, it is often desirable to connect removable circuit boards, typically referred to as printed circuit cards or daughter boards, which include electronic components and appropriate circuitry for performing a specific function, to a mother board in a particular electronics application. Such an arrangement greatly facilitates the replacement of various types of circuit modules within the mainframe of the application, either for modification of the mainframe function or repair or replacement of defective circuit modules.
In this environment, it is not uncommon for a particular daughter board to have a large number of terminals that must be connected to a corresponding number of terminals on the mother board. In the past, the connection of individual circuits between the boards was accomplished by providing one of the boards, usually the daughter board, with a plurality of pins, one for each circuit, and by providing the mother board with an equal number of recesses or holes into which the pins were inserted during connection of the boards. This arrangement was satisfactory with installations in which the boards were intended to be connected relatively permanently, or at least where they were to be disconnected very infrequently.
However, this arrangement was not satisfactory in installations in which the daughter boards were changed or replaced with some degree of frequency, as in the case of a generic motherboard with custom daughter boards having a specific mission profile. With a multiple pin connection, a certain minimum amount of force between the pin and a contact within the receptacle into which the pin is inserted is required to maintain engagement and to assure that good electrical contact is maintained at all times.
The problem that develops is that during insertion and removal of the boards, the force that is established between the pins and the receptacle contacts eventually causes deleterious wear on the pins and the contact surfaces, resulting in poor electrical contact from uneven mating of pin and contact surfaces. Also, the rubbing contact between the pin and contact surfaces during insertion and removal of the pins tends to promote the accumulation of dirt and/or coatings which adversely affect electrical contact.
Another significant disadvantage of multiple pin connectors is that the force necessary to cause the insertion of the pins into the receptacles can render the physical connection difficult to accomplish and can damage the pins. It will be appreciated that, while the force required to connect or disconnect one pin into or from one receptacle may be relatively small, for connectors having a hundred or more pins, the force becomes quite considerable. For example, standard mother board/daughter board connectors have an individual mating force of from 2.5 to 4 ounces per pin; this equates to 15 to 25 pounds of force required per hundred pins, for both connecting and disconnecting. Since some high density computer modules today have as many as 250 to 300 pins, it will be apparent that very considerable force may be required to make a particular connection, and further that the force required for disconnection may be so great as to require a tool to effect the disconnection of two boards, with the attendant risk of bending pins or otherwise damaging one of the boards.
A major solution to the foregoing problem has been the advent of zero-force connectors, of which several have been developed and can be found in the art. The salient feature of the zero-force connector is that, whatever the form of the electrical contact elements on the respective boards being connected, there is no force applied therebetween during the actual connecting and disconnecting movements of the respective boards. Unfortunately, prior art zero-force electrical connectors that have been developed and are commercially available, all have certain deficiencies and disadvantages that render them unsatisfactory in most electronic mother board/daughter board applications. Many are not actually zero-force connectors, but rather are reduced force connectors, in which the sliding contact force between contacts on either board, encountered during connection and disconnection of the boards, is reduced to a lower level than that which is established after full connection is made and which is maintained until the boards are disconnected. Other connectors, which are truly zero-force, are very complicated and costly, a factor which takes on major economic proportions in view of the vast quantities of boards utilized in modern day computer manufacturing. Some require the use of tools to generate sufficient force after connection to provide good physical connection and electrical contact, thereby perhaps preventing the insertion and removal of daughter board cards by users of the equipment, and even making the insertion and removal difficult for service personnel. In addition, most prior art zero-force connectors are for individual circuits without providing electrical shielding or impedance control.
Thus, there is a need for a simple, inexpensive, yet highly efficient and effective zero-force electrical connector for use in connecting printed circuit card modules to mother boards in sophisticated electronic applications.